JacobAziza -
When I was on a business trip in Brussels in 2007 I got to drive this :
2004 Renault Megane Sedan with 1.9 liter dCi engine
One nice thing (assuming the ScanGauge was reading correctly), was that when I pulled my foot off the accelerator pedal
in gear, the Scangauge showed 9999 MPG, meaning DFCO (deceleration fuel cutoff) mode was present.
What I am implying is, with a modern diesel drivetrain, P&G should give you infinite MPG during the (in gear) coast.
CarloSW2